1. Field of the Invention
The present invention relates to a melt composition used for growth of a gallium nitride single crystal and a method for growing a gallium nitride single crystal.
2. Description of Related Art
Gallium nitride has been attracting a great deal of attention as a superior blue light emitting diode, and has been practically used in material for a light emitting diode or a semiconductor laser diode. In recent years, a method for growing a gallium nitride single crystal from a melt by flux method has been receiving particular attention.
International Publication No. WO 2004/013385 A1 discloses that GaN single crystals are grown using a melt composition of a Ga—Na-A (Li, K, Rb, Cs, Fr)—B (Ca, Sr, Ba, Ra) system by flux method. In this regard, however, one or more element(s) are selected from at least one of the A group elements or the B group elements.
Further, International Publication No. WO 2004/067814 A1 discloses that GaN single crystals are grown using a melt composition of a Ga—Li-A (Na, K, Rb, Cs, Fr)—B (Ca, Sr, Ba, Ra) system by the flux method. In this regard, however, one or more element(s) are selected from at least one of the A group elements or the B group elements.
Still further, U.S. Pat. No. 5,868,837 discloses growth of GaN single crystals using a melt composition of a Ga—Na-A (A represents a small amount of alkaline earths) system by means of the flux method. An additive amount of the alkaline earths is defined such that 0.002 to 0.05 mol is contained per 1 molar quantity of Ga. Strontium is used in Example 2, while barium is used in Example 3. In each of the Examples, an inner lining composed of tungsten is provided on the interior of a pressure-resistant vessel formed of stainless steel, and raw materials are charged therein.
In growth of GaN crystals by means of Na flux method, addition of Li to a melt has been known for increasing flatness or transparency of the crystals (Jpn. J. Appl. Phys. 42 (2003) L565).
Further, it is also known that when an additive amount of Li is greater, Li is introduced into the GaN crystals (Conference Proceedings I, 7a-X-7, the 66th Autumn Meeting, 2005, The Japan Society of Applied Physics). Such introduction of Li into the GaN single crystals will result in an increase of impurity band emission having a central wavelength of approximately 511 nm when the PL (Photo Luminescence) or CL (Cathode Luminescence) is measured.